Help me and my friend out

Okay so there was this guy whom my friend added and now this guy which is 18 (and my friend, 15) wants to have a relationship with my friend now. She tried being sorta rude to him in the hopes of swaying him off but it didnt work. Mind you this guy has no friends , supposedly a nerd in his school and my friend is apparently the first girl to "accept" him. She's getting pretty sick of him trying to have a relationship with him but don't know what to do and I don't know what to do so I here I am asking you guys. All of your replies are much appreciated.

Block him on everything and ignore any attempt. If he seems dangerous, ask parents or teachers for help.
What do you mean by sort of rude? Has she made it clear that she doesn't want a relationship or anything to do with him in that matter?